Studies Of The Difference Of Salt Resistance Of Black Iocust Clones

Six clones of black locust (Robinia pseudoacacia) W₁,L₁,L₅₉,L₇₈ ,D₃₂₇ and D₅₆ were tested in order to study the differences of their abilities of salt resistance and effects on growth ,photosynthesis and osmotic adjustment of the clones by pot experiments. Two tests were conducted:one by continual adding NaCl salt solution,and the other by a long term soil drought stress after adding salt. The main results were as follows: Test I: Black locust clones have different abilities of salt resistance。According to the results of comprehensive appraisal analysis of some important indexes by coordinate integrative assessment,salt resistance abilities of six black locust clones under T₁,T₂,T₃ treatments were irrespectively ranked as follows:W₁>D₅₆>L₅₉>L₇₈>D₃₂₇>L₁;W₁> D₃₂₇> D₅₆>L₅₉>L₁>L₇₈; D₅₆>W₁>L₅₉> L₁> D₃₂₇ >L₇₈. Salt stress obviously suppressed the growth of the black locust clones,but growth amount of W1 and D₅₆ among them was relatively heavy. W₁ meeted salt adverse circumstance by speed-growth in the initial stage. Salt stress raised root-stem ratio of all clones,which of D₅₆ improved most among them,namely effect of salt stress on the ground part was greater than effect on the underground one . In the initial stage of salt stress, Pn of black locust clones had not suppressed. With increasing times of adding salt, Pn begun to decrease speedly and aggravated further with improving of salt concentrations。L₁ and L₇₈ ,D₃₂₇ and L₁,D₅₆ and L₁ reached irrespectively higher Pn under T₁,T₂,T₃ salt treatments. Salt stress dropped Tr and Cond , but there were not remarkable difference among black locust clones;Salt stress reduced Chla ,Chlb ,Chla+b contents and Chla/b ratio , and furtherly reduced with improving of salt concentrations,the differences among the salt gradients were not remarkable. The changes of Pn were the result of mutual action of the above facts. Salt stress increased the conductivity of black locust leaves , and contents of MDA ,Pro and the soluble sugar ; at the same time it reduced the content of Protein . The values of the above indexes fluctuated during treatment. Study results indicated what played a main role in organically osmotic adjustment was soluble sugar。The sequense of organically osmotic adjustment was L78> L1 >W1> L59> D327>D56。The characteristics of Na+,K+,Ca2+,Mg2+ distribution of black locust clones were irrespectively:stem >root >leaf;leaf >stem >root;leaf >root >stem;root >leaf>stem.. Studies showed that the clones went on osmotic adjustment through actively absorbing various kinds of ions under light salt stress;holding back Na+ and alternatively absorbing mineral nutrition ions, keeping mineral nutrital balance under heavy salt stress. Badly holding-back Na+ ability of stem and high-level Ca2+ of root made L78 not bear salt stress. Well control-absorption of ion and keeping nutrital balance were the reason that W1 and D56 had steady ion content and better salt resistance. Studies showed that the sequense of inorganic osmotic adjustment was D56>W1>D327> L59> L1>L78。In the initial stage of salt stress ,inorganic ion in osmotic adjustment played a main role ;With the continuation of salt stress,the function of organic osmotic adjustment strengthened。Under salt stress , K+/Na+,Ca2+/Na+,Mg2+/Na+ ratio increased in root and leaf and decreased in stem;salt stress promoted stem alternative transportion to K+,Ca2+,Mg2+,and suppressed leaf alternative absorption to K+,Ca2+,Mg2+。Studies showed that the dropping of leaf alternative absorption of K+,Ca2+,Mg2+ was the result of Na+ competition and suppression to other ions. W1 and D56 could keep mineral nutrital balance better, especially its root and top leaf,but L78 couldn't bear salt stress,and well maintained mineral nutrital balance。Testâ…¡:The three clones had different sequences of drought and salt resistance under different stress intensities. Namely â‘´under middle and heavy drought stress,their orders were D327>L78>W1,D327>W1> L78 respectively; ⑵under middle and heavy salt stress,their orders were L78>D327>W1,D327>W1>L78 respectively;⑶under middle droughr-salt and heavy-drought –middle-salt stress ,their orders were L78>D327>W1,D327 >W1> L78 respectively;â‘·under middle-droughr and heavy-salt ,heavy drought and heavy salt stress,their sequences were W1>D327> L78,W1> L78>D327. Soil moisture of adding-salt groups reduced more slowly than that of not-adding-salt group,because salt in the soil has increased inhibition of drought stress to transpiration. The sequence of water consumption of the clones was W1>L78>D327, but the sequence...